The present invention relates to a circuit configuration for a slip-controlled vehicle brake system which is equipped with sensors for the determination of the rotational behavior of the front and the rear wheels including electronic circuits for the processing, logic combining and monitoring of the sensor signals. The invention provides for the generation of control signals which allow control of the braking pressure variation individually at single wheels and/or simultaneously at several wheels according to predetermined selection criteria.
A known circuit configuration of this type (German printed and published patent application No. 22 09 745) comprises circuitry for monitoring the wheel sensors which serves to de-activate the entire brake slip control upon the occurrence of a sensor error. If this happens during a braking action or if the driver does not recognize such sensor malfunction in time, a dangerous situation may result from the de-activation of the brake slip control.
It is also known to monitor the pressure of the auxiliary energy source in an anti-locking vehicle brake system and to de-activate the brake slip control in the event of pressure decrease which occurs not instantaneously, but upon termination of the existing control signal by means of a bridging circuit (German patent specification No. 24 11 173). This system recognizes that in a defective auxiliary circuit the residual pressure frequently is still sufficient to complete the prevailing braking action with control. Such considerations are not applicable to the monitoring of sensors because the malfunctions thereof are of immediate consequence.
Previously, it has been considered necessary to de-activate the slip control at once or with delay in the event of sensor failure or sensor malfunction in order to reliably preclude braking pressure decrease as a consequence of interference signals and in order to ensure at least braking of the vehicle without slip control even in an interference. To this end, it should be recognized that a faulty sensor might fake wheel lock and thus provoke dangerous braking pressure decrease. The disadvantages and serious consequences of an unexpected de-activation of brake slip control, for instance during braking with slip control on icy roads, have been a problem in these prior art systems.
Hence, it is an object of the present invention to overcome the disadvantages of the prior art slip-controlled vehicle brake systems and to provide a slip-controlled brake system which completes the braking action without endangering driving stability. The present invention is directed to optimum short stopping distance even upon the occurrence of a sensor error of short or longer duration or a defect in the path of transmitting and processing of the sensor signal such as, for example, in the event of cable fraction, cable shortcircuit, a defective trigger or the like. That is, instantaneous de-activation of the control should be avoided because of the described dangerous consequences for driving stability and without significantly reducing the braking effect.